Normal Map Cycles Baking Help
Plug your texture image into the displacement shocket on the material output node. You can add a (converter>>math>>multiply) node between them to adjust the strenght.

Edit.
Excuse me. I forgot that the "selected to active" means the active doesn't count, just the selected. So what you can do, duplicate the lowpoly object, than select all three model. This method gives much better result with Blender render.